Electric induction furnace for continuously heating metal strip



- p -'16, 1947. G. P. WILSON 2,427,485

ELECTRIC INDUCTION FURNACE FOR CONTINUOUSLY HEATING METAL STRIP FiledAug. 21, 1943 I N VEN TOR.

Golder T Vz'lson BY 2s ATTORNEY Patented Sept. 16, 1947 ELECTRICINDUCTION FURNACE FOR CON- TINUOUSLY HEATING METAL STRIP Golder P.Wilson, Alton, Ill., assignor to Olin Industries, Inc., a corporation ofDelaware Application August 21, 1943, Serial No. 499,527

Claims. 1

This invention relates to the continuous heating of metal strip andparticularly to the heating of metal strip by means of electricinduction.

It has heretofore been well known that heating of metal can beaccomplished by electric induction by employing the transformerprincipal in which a primary coil is supplied with alternating electriccurrent, and the metal to be heated, when placed in inductiverelationship with the primary coil, is heated by its resistance to theinduced electric or magnetic current.

Methods and apparatus having various means for bringing the metal intoinductive relationship with the primary coil have been describedheretofore. For instance in one method of heating metal strip, the stripwas continuously passed in an axial direction through a primary coil,the metal being heated by the locally induced magnetic and electric eddycurrents. Such methods and apparatus have the disadvantage however, thatwith high conductivity non-magnetic strip it is difiicult to induceelectrical eddy currents of sufficient magnitude to bring the strip toan effective treating temperature.

According to other methods, the metal in the form of wire, or coiledrod, was fed in the path of a helix around or through a primary coil,but such methods and apparatus have among others the disadvantage of notbeing suitable for use with wide strip, due to the difiiculty involvedin forming such strip into a helix.

According to still another method described for heating metal in theform or wire or strip, two such wires were continuousl passed inparallel paths on opposite sides of a primary coil. A completeelectrical secondary circuit about the primary coil through the wireswas provided by means of contact bars having rollers on their ends inelectrical contact with the moving wires. Such methods and apparatus, inwhich contact bars, brushes and the like are employed, have thedisadvantage in some instances that contact parts are subject toexcessive wear requiring frequent replacement and that an appreciableportion of the induced current is consumed by the contacting means.

All such prior methods and apparatus for the electric induction heatingof metal have been attended by one or more serious disadvantages and itis an object of this invention to provide an im proved apparatusovercoming all such objections.

Another object of this invention is to provide an improved apparatus forthe efiicient and economical heating of metal strip by electricinduction.

Another object of the invention is to provide an efficient electricinduction furnace for economically effecting the continuous heattreatment of metal strip.

Still another object of the invention is to provide an electricinduction furnace suitable for the heating of magnetic or non-magneticmetal strip of either high or low electrical conductivity.

Other object and advantages will become apparent from the descriptionand accompanying drawing, in which Figure 1 is a diagrammatic view of anelectric induction furnace illustrating one embodiment of thisinvention,

Figure 2 is a diagrammatic view of an electric induction furnaceillustrating another embodiment of this invention, and

Figure 3 is a sectional view of a contact roll illustrating anembodiment of this invention,

The above objects and advantages are accomplished in accordance withthis invention by providing a novel process and apparatus in which themetal to be heated in strip form is passed over metal contacts which inturn are electrically connected by means of a liquid conductor, and anelectric current is induced in the electrical loop formed by the movingstrip, contacts and liquid conductor. It has been found that veryeiiective and efficient heating can be accomplished in this manner sincecurrents of high amperage and relatively low voltage can be induced inthe strip with practicall no loss of power due to the contacting andconnecting means.

Referring to the drawing, Figure 1, in one embodiment of the invention,the metal strip I, advanced by any suitable means, is passed over ametal contact roll 2, up over rolls 3 around the primary coil 4, andover contact roll 5 on the discharge end of the furnace. The primarycoil 4 is provided with leads 6 and laminated iron core I. Contact roll2 having an axle 8 is provided at its ends with metal projections 9 andH! and contact roll 5 having axle H is provided at its ends with metalprojections 12 and 13. The projections 9 and I2 are at least partiallysubmerged in the conducting liquid I l held in container l5 and theprojections i0 and I3 are at least partially submerged in the conductingliquid (4 held in container IS. The contact rolls 2 and 5 are thuselectrically connected by the liquid conductor M at both ends of thecontact rolls, and a complete secondary electric circuit is providedaround the primary coil t in the loop formed by the moving strip,contact rolls and liquid conductor. The strip l is bent around asubstantial portion of the surfaces of contact rolls 2 and 5 by passingit over rolls 24 and so that a large area of contact is provided betweenthe strip and contact rolls with good electrical connection and lowamperage per square inch of contact surface to prevent arcing andconsequent burning of the strip,

An alternating current, which may be of either high or low frequency or,for instance any of the available standard commercial frequencies, isapplied to the primary leads 6 and the strip i is heated by the currentinduced in the loop. The contact rolls, liquid conductor, and rollscontacting the strip in the loop are insulated from any supporting metalframe-Work in order that all the induced current will flow through themoving strip instead of being short-circuited through such frame-work.

The temperature of the strip can be regulated either by varying thespeed at which the strip travels or by varying the power supplied to theprimary coil 4. For instance, employing an in duction furnace designedas described above, yellow brass strip about 5.663 inches wide and 0.012inch thick may be passed through the furnace at the rate of about 17.3feet per minute with a power input to the primary coil 4 of about 18.4kilowatts per hour to yield about 233 pounds of brass strip heated to atemperature of about 700 C. per hour.

In another embodiment, illustrated in Figure 2, the strip 1 is advancedover a contact roll El, down thtrough pinch rolls 18, around the pri--mary core 23 which carries the primary coil H), with leads 22 up throughpinch rolls 2i} and finally over contact roll 2|. Contact rolls l7 and2| are electrically connected by means of a liquid conductor, forinstance held in container 3 l. The pinch rolls l8 and 213 may beoperated, for instance, in conjunction with the strip advancing means toprovide the desired tension on the strip as it passes over contact rollsH and 2! while maintaining the strip substantially without tensionbetween the pinch rolls l8 and 2t as it passes through theelectromagnetic field set up by primary IQ. In this embodiment of theinvention, with heavy metal strip, however, a good contact electricalcontact between the strip and contact rolls is ordinarily obtained dueto the weight of the metal and no auxiliary means such as the pinchrolls l8 and 20 are essential in order to obtain the necessary contactwith the contact rolls. It is desirable, however, to provide arelatively large surface of contact between the strip and contact rolls,for instance b passing the strip over rolls 2% and 21,

Any suitable means may be employed for inducing a current in thesecondary loop, provided that the current is of suflicient magnitude toheat the strip to the desired temperature. For instance, the primarycoil may be wound on a leg of the core outside the loop, Figure 2, or onthe leg of the core inside the loop, as illustrated in Figure 1, or thecore may be omitted and the primary coil disposed within the loop.

The contact rolls such as indicated at 2 and 5 of Figure l and at I"!and 21 of Figure 2, may have any suitable form, but in the preferred embodiment illustrated in Figure 3, they have a contact portion 233 and aspaced cup-like flange or projection 29 at one or both ends of the roll,the contact portion and flange being carried by any suitable axle 3B.The flange 29 is at least partially submerged in the liquid conductorand hus provides a connection of low resistance between the liquidconductor and strip through the contact portion 28 of the contact rolls.With such construction it is possibl to avoid any contact or wetting ofthe strip itself with the liquid conductor. The 1iquid conductor may beapplied in any suitable manner to provide the electrical connectionbetween the contact rolls, for instance the liquid conductor may beemployed at only one end of the contact rolls instead of at both ends.

The liquid conductor employed may be any suitable molten metal or liquidsuch as mercury, Woods metal, or any suitable electrolyte or othersuitable fluid. In operation it is ordinarily dcsirable to confine suchliquid conductor M in the containers such as l5, l6 and 3|, andclose-fitting covers may be provided for this purpose.

The induction furnace of this invention may be employed to heat metalstrip of either high or low electrical conductivity for instance in anannealing operation or in any other operation in which it is desired tocontinuously or semicontinuously heat metal in strip form. The hot stripmay be cooled in any suitable manner depending upon the speed of coolingnecessary to give the desired physical properties of the metal and, ifit is desired to pickle the strip after it is heated, such pickling maybe accomplished for instance by passing the strip through a suitablepickling bath as it leaves the furnace.

The heating of more than one strand of metal may be readily accomplishedin accordance with this invention, for instance by providing contactrolls for each of such strands and so connecting the liquid conductorsaccompanying the contact rolls that the moving strands are electricallyconnected in series, or parallel as desired, with respect to the primaryinduction means. Similarly more than one strand of the metal may beheated by simultaneously passing a plurality of strands over contactrolls, either with one on top the other, for example in forminglaminated sheet or the like or, for instance with narrow strands, sideby sid in parallel paths. The word strip, therefore, is used indescribing the invention herein and in the claims in a sense inclusiveof one or more strands of the metal to be heated.

This invention accordingly provides means for the continuous heating ofmagnetic or non-magnetic metal strip of either high or low electricalconductivity in the form of flat strip having any desired width, wire,or the like and has a wide held of utility without being subject to allthe disadvantages and limitations attending prior processes andapparatus.

It is to be understood that the embodiments of the invention as shownand described herein are only illustrative, and that many changes may bemade therein without departing from the spirit and scope of theinvention as set forth in the following claims.

Having thus described the invention, what is claimed and desired tosecure by Letters Patent 1. In an electric furnace for heating metalstrip, the combination comprising a liquid electrical conductor, spacedmetal rolls having stripcontacting portions and separate portionscarried in and electrically connected by said liquid conductor, meansfor advancing said strip in contact with said rolls, means forestablishing an alternating electromagnetic field, and means for guidingthe portion of the strip between said rolls through and in inductiverelation to said field.

In an electric furnace for heating metal strip, the combinationcomprising a liquid electrical conductor, spaced metal rolls havingstripcontacting portions and separate portions carried in andelectrically connected by said liquid conductor, means for advancingsaid strip in contact with said spaced rolls, means for holding saidmoving strip in contact with a substantial portion of the contactsurface of said spaced rolls, means for establishing an alternatingelectromagnetic field, and means for guiding the portion of the stripbetween said rolls through and in inductive relation to said field.

3.111 an electric furnace for heating metal strip, the combinationcomprising a mercury bath, spaced metal rolls having strip-contactinportions and separate portions carried in and electrically connected bysaid mercury bath, means for advancing said strip in contact with saidrolls, means for establishing an alternating electromagnetic field, andmeans for guiding the portion of the strip between said rolls throughand in inductive relation to said field.

4. In an electric furnace for heating metal strip, the combinationcomprising a liquid electrical conductor, spaced metal rolls havingstripcontacting portions and separate portions in and electricallyconnected by said liquid conductor, means for advancing said strip incontact with said rolls, means for establishing an alternatingelectromagnetic field, means for guiding the portion of the stripbetween said rolls through and in inductive relation to said field, anddriven. pinch rolls between and adjacent to each of said spaced metalrolls for maintaining the hot portion of said strip substantiallywithout tension.

5. In. an electric furnace for heating metal strip, the combinationcomprising a liquid electrical conductor, a metal roll on the charge endand a metal roll on the discharge end of said furnace for contactingsaid strip, said rolls having end portions carried in and electricallyconnected by said liquid conductor, means for advancing said strip incontact with said rolls, means for establishing an alternatingelectromagnetic field, and means for guiding the portion of the stripbetween said rolls through and in inductive relation to said field.

GOLDER P. WILSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

